1. Field of the Invention
Embodiments of this invention relate generally to disk drives of the type generally used for storing digital data, and in particular to methods and devices for parking the heads used in a disk drive at a constant velocity, and disk drive systems incorporating the same.
2. Description of Related Art
Modern computers require media in which digital data can be quickly stored and retrieved. Magnetizable (hard) layers on disks have proven to be a reliable media for fast and accurate data storage and retrieval. Disk drives that store and retrieve data from hard disks have thus become popular components of computer systems.
FIG. 1 illustrates a conventional disk drive system that could be used to implement embodiments of the present invention. FIG. 1 shows a disk drive system 2 comprising a disk drive microprocessor 4, control logic 6, voice coil motor driver 8, voice coil motor 10, head assembly 12, read/write heads 14, hard disks 16, spindle motor 18, and spindle motor drivers 20. In operation, a computer 22 communicates through controller 24 with the disk drive microprocessor 4. In response to commands from the controller 24, the disk drive microprocessor 4, by means of control logic 6, activates voice coil motor driver 8. The voice coil motor driver 8 energizes the voice coil motor 10 to position the head assembly 12 and read/write heads 14 over specific track locations on the hard disks 16, which are rotating at a substantially constant velocity under the impetus of the spindle motor 18 and spindle motor drivers 20. Once the read/write heads 14 have stabilized over the appropriate tracks, the read/write heads 14 can read data from, or write data to, the hard disks 16.
Those skilled in the art will recognize that the disk drive system 2 of FIG. 1 is not intended to limit embodiments of the present invention. Indeed, those skilled in the art will recognize that alternative hardware configurations may be used without departing from the scope of the present invention.
In typical disk drive systems, the hard disks rotate at high velocities and read/write heads are positioned over the hard disks with very little air gap separation. In this configuration, read/write head contact with the hard disks (a head crash) can be catastrophic. Data can be permanently lost, or the read/write heads or hard disks can be damaged such that the entire disk drive system no longer functions. Therefore, modern disk drive systems avoid head contact with the hard disks as much as possible. To minimize read/write head contact with the hard disks, many disk drives park their read/write heads when the disk drive system is powered down so that the read/write heads rest over a parking zone (an area on the hard disks where no data is stored, typically the innermost central region of the disks) instead of an area used for storing data. The use of a parking zone minimizes wear on the recording area of the disks and thus increases the reliability of the disk drive system and the integrity of the stored data. Head parking circuitry activates when the disk drive system is being powered down or when the hard disks temporarily stop spinning. Such circuitry energizes the voice coil motor and moves the read/write heads to the parked position on the hard disks.
FIG. 2 illustrates a conventional head positioning system that includes a head parking system. Under normal operating conditions where data is being written to or read from the hard disks, a voice coil motor driver 8, consisting of a first driver 8a and a second driver 8b, produces a current flow through a voice coil motor 10. This current flow magnetizes a voice coil 10a, and causes the voice coil 10a to push or pull on a fixed permanent magnet 10b surrounding the voice coil 10a. These forces of repulsion or attraction cause the voice coil 10a to move in relation to the fixed permanent magnet 10b. Because the voice coil 10a is fixedly attached to the read/write heads 14 through the head assembly 12, movement of the voice coil 10a results in movement of the read/write heads 14 in relation to the hard disks 16.
Activation of the parking circuitry is triggered by the application of a park voltage source 26 to the voice coil motor 10 through a park voltage resistive network 28. The park voltage source 26 is typically generated by stored energy in the spindle motor 18 or a storage capacitor 18a When the park voltage source 26 is applied, a constant current is sourced through the voice coil motor 10, which magnetizes the voice coil 10a and results in movement of the voice coil 10a and fixedly attached read/write heads 14 towards the park position.
However, the constant current provided by the park voltage source 26 causes the read/write heads 14 to accelerate towards the park position, creating high gravitational forces and mechanical stress on the head assembly 12. Acceleration of the head assembly 12 and gravitational forces can be minimized if the read/write heads 14 are parked at a constant velocity. Constant velocity parking will drastically reduce the chance of head slap (heads slapping on the disc) and resultant media defects.
One proposed way of parking read/write heads at a constant velocity is disclosed in the Carobolante patent (U.S. Pat. No. 5,566,369), incorporated herein by reference, which uses a feedback loop comprised of an active component (op amp) and resistors to maintain a constant voltage across the voice coil. In Carobolante, knowledge of the resistive component of the voice coil is necessary to select proper resistor values.